The voting system is basically a contest of who can get there votes in early. So, if you vote on a post, predicting that there'll be large votes coming in after, you'll maximize your curation rewards.

I have also noticed that the posts of authors who keep coming back to the trending page, get high rewards among the newly created posts only after a few minutes. How does that work? Most of the time they only get votes, but nobody comments on these posts. So I think that these posts are probably not even read. In my opinion this is fraud!

This is what I was trying to say, currently curation is very inefficient. A lot of those votes are autovotes, so the voters have set to vote for the same people over and over again. Voters can choose to vote however they wish, of course, but that's just bad curation that as you point out demoralizes newcomers. Instead, it'd be much better if the voters delegated to curators who will find the good, unrewarded posts.

Another example is why has somebody with 65K HP (@curie) a higher vote value than somebody with 78K HP (@krnel)?

This is just the base amount the accounts have powered up. Then, there are delegations and follows, which add on to the vote. You'll see that @curie has an additional +200K in delegations, so that adds on to @curie's base vote. And then there are other accounts following, which add another +2M on average through Hive.vote. If you can get in between @curie and these Hive.vote votes, then you'll stand to maximize your curation rewards.

I know it can all be strange for newcomers, and it is indeed a weird system. I'd like to see the system overhauled, but until that happens, my point stands - we need to support curators with HP.